Volume-control system



June 10, 1930.; R, ATHES 1,762,727

VOLUME CONTROL SYSTEM Filed Dec. 15, 1927 2 Sheets-Sheet 1 //v VE/V 70R;ROBERT 6. M47715? Emma 10, 1930., Q, MATHEs 11,732,77

VOLUME CONTROL SYSTEM Filed Dec. 15, 192'? 2 Sheets-Shaw 2 markedaccordingly, and thesemarkings serve Patented June 10, 1930 UNITEDSTATES PATENT OFFICE ROBERT O. MATHES, OF 'WYOMING, NEW JERSEY, ASSIGNORTO BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., ACORPORATION OF NEW YORK voLuME-ooNrRoL sYs'rEm Application filedDecember 15,1927. Serial No. 240,105.

This invention relates to sound recording .and reproducing systems andmore particularly to volume control for such systems.

The object of the invention is to provide 5 novel methods of extendingthe effective range of sound recording and reproducing systems.

Due to the limitations inherent in record ing material and apparatus, itis impractical to record a volume range much in excess of 40 TU withoutemploying some form of volume compression. Heretofore, it has beenproposed to increase the volume range of recording and reproducingsystems by recording a uniform intensity and making a second record ofthe variations necessary to obtain uniform intensity. The second recordthen serves as a volume control during reproduction and restores thelevel of each part of the first record to its proper relative level. Inaccordance withthis invention only one record is made but the loss inthe recording circuit is varied from time to time to keep the soundlevel within the recording limits. When such changes are made the recordis to effect compensating changes of sound level in the reproducingcircuit.

The method of marking the sound record may take any one of variousforms, that is to say, changes in the amount of compression used may berepresented in'various ways such as by different intenslties, diflerentfrequencies or difi'erent lateral locations.

While the general features of this invention have been stated above, theinvention will be more eas ly understood by referring to the followingdetailed description of one of its particular embodiments as illustratedin the accompanying drawings. These drawings are based on that method ofrecording wherein different lateral locations of the indicative marksare used to represent various amounts of volume compression. Fig. 1illustrates in diagrammatical form the arrangement of the apparatus usedin recording and Fig. 2 shows a somewhat similar disposition of theapparatus adapted for reproducing.

The operation of the invention during the recording process will now bedescribed.

Sound vibrations emanating from the sound source 1 are picked up andtranslated into electric currents by the microphone 2. These currentsare amplified by amplifier 3,v conducted over wires 1 and 5 andimpressed upon that part of potentiometerfi, consisting of resistances 7to 13 in series. During normal operation, that is, when no compressionis required, relay 14 is in its actuated position. A circuit includingcontact 15 of relay 14 and conductors 4, 16 and 18 is then complete fromthe potentiometer resistances already enumerated to recording device 17,and it is evident that the full voltage impressed upon the potentiometeris also applied to the recording device in projection machine 76. I

he recording operator who follows the musical score may observe that asound peak is about to be reached and that it will be necessary toinsert say a 10 TU loss in the recording circuit. He thereupon actuateskey 19. The operation of this key first closes contacts 20 and 21,thereby preparing a path from the'upper contact 31 of relay 22 throughcontacts 20 and 21 to wires 23 and 24 which lead to recording lamp 25and the Winding of relay 26, and the recording lamp 27 and the windingof relay 28 respectively. After these circuits have been preparedcontact 29 of key 19 closes, completing the operating circuit of relays22 and 30 from ground through contact 29, through the relay windings inparallel to grounded battery. Relay 30, however, is slow acting and doesnot operate at this time. i The operation of relay 22 completes thecircuits prepared above by grounding its upper contact 31. The recordinglamps 25 and 27 will then be flashed simultaneously to record on thefilm two spots in the positions chosen to indicate that a 10 TU loss isbeing inserted in the recording circuit. Relays 26 and 28 will also be 0erated upon the grounding of contact 31 since they are in parallel withlamps 25 and 27 respectively. The operation of relay 22 also completes acircuit for relay 32 extending from grounded battery through conductor33 and winding of relay 32 to ground. v

The operation of relay 32 opens the circuit extending from batterythrough the upper make contact 34 of relay 35, through upper breakcontact 36 of relay 32, through the upper make contact of relay 14, toground through the winding of that relay causing it to release. Theupper contact 37 in closing locks relay 32 in its operated position overan obvious circuit. Relay 32 also completes the operating circuit ofrelay 35 from grounded battery, through contact 38, relay winding andcontact 39 of relay 32 to ground. Relay 35, however, is slow acting anddoes not operate at this time.

The relays 26 and 28 having been operated, a locking circuit from groundthrough contact 40 of relay 41, conductor 42, contacts 43 and 44, andrelay windings to grounded battery isnow complete and relays 26 and 28are locked up. The upper contacts of these relays are in parallel withkey contacts 29 and serve no. useful purpose during recordmg. Operatingcircuits are also complete for relays 45 and 46 from contacts 43 and 44through relay windings to grounded battery. Sl w actingrelay 30, whichhas already been energized, is so timed that it operates a short timeafter relays 26 and 28. The operation of this relay deenergizes relay 22by disconheating the battery at its lower contact and relay 22 in itsturn opens the operatlng c1rcuits previously made, namely, those ofrelays 26, 28, and 32 and those'of recording lamps 25 and 27. It shouldbe remembered, however, that while the lamps are extinguished after onlya momentary flash, the relays are held operated by their lockingc1rcuits. 1

Slow acting relay 35 is arranged to close its contacts and lock upthrough contact 54 about .02 second after its operating circuit whichhas already been traced, is made. In closing, this relay opens contact34, thereby releasing relay 32 which has already been held operated I asufiicient time to insure the release of relay 14. The operating circuitfor the potentiometer relay 47 is now complete and is traced fromgroundedbattery through contact 38 of relay 41, contact 48 of relay 35,

contacts 49 and 50'of relays 45 and 46, which have already beenoperated, contact 51 of relay 52, conductor 53, and winding of relay 47to ground.

The operation of relay 47 restores the recording circuit opened by relay14 and completes a locking circuit for itself prepared by the operationof relay 35 and extending from ground through contact 55, conductor 56,contact 57 of relay 35 to grounded battery. The release of relay 32 byrelay 35 closes contact 36 to prepare, for the next operation, apathyfor the holding circuit of-the potentiometer relays and completes acircuit for relay 41, from the battery through winding of relay 41,contact 58 and contact 59, to ground. The operation of relay 41 opensthe holding circuit of relays 26 and 28 and the operating circuits ofrelays 45 and 46 at contact 40, causing these relays to release. Byopenmg contact 38 re lay 41 also releases rela 35 whlch opens theoperating circuit of re ay 47 at. contact 48,v

tentiometer relay 47 is operated instead of potentiometer relay 14. Itwill be remembered that the recording circuit was opened by relay 14which was released when key 19 was first actuated. At its lower contact60, relay 47 recloses a circuit through resistance 61 for the recordingdevice 17. The full volume of the output ofamplifier 3 is, however, nolonger impressed upon the recorder since resistance 7 no longer forms'zapart of the recording circuit. I This circuit now extends fromrecording'device 17, through conductor 18, resistances 13 to 7, 61,contact 60, conductor 16, to recording device 17.

The operation of the recording mechanism thus far described consiststhen in actuating the proper key to introduce the desired loss in arecording clrcuit. This is accomplished by first releasing the lastpreviously operated potentiometer relay to momentarily open therecording circuit, and then closing the circuit again at the properpoint along the potentiometer winding to give the desired change involume level. I

When it becomes necessary to again modify the volume level another keyWill be actuated and another cycle of operations will occur in a mannersimilar to that already described. A different combination of the relays26, 28 and 62 will be energized and a diflamps to mark the filmaccordingly. In this way, a complete record of a musical selection isrecorded upon the film. By properly adjusting the volume level from timeto time during reproduction from this record the entire composition isreproduced at its original volume throughout.

The reproducing apparatus for making these adjustments automatically issubstantially a duplicate of that shown in Fig. 1 except that the keys65, 19, etc. are omitted, the recording lamps are replaced by contactfingers 66, 67 and 68 and the microphone 2 is replaced by a loud speaker69; A copy of the sound record is perforated according to the markingsmade on it during recording before being inserted in the projectionmachine 70, wherein a source of light, (not shown) actuates aphotoelectric cell 71, through the film 72, in the well-known manner.Current variations are then amplified and impressed upon the loudspeaker in the usual way.

As in the recording process, the output of the amplifier 3 is impressedupon the series of resistances 7 to 13 of potentiometer 6. For normaloperation in reproducing, however, the loud speaker is not copnecteddirectly in parallel with the amplifier. Instead it is connected acrossonly-resistance 13 by means of relay 14. Accordingly when the projectionmachine is reproducing those parts of the record in which there is nocompression, there is a 60 TU loss in the loud speaker circuit. Whenthat part of the film in which was a 10 TU loss reaches the contactfingers, fingers 66 and 67 which correspond to the recording lamps 25and 27 in the recording apparatus, will move into the perforations inthe film and close their contacts. Circuits are then complete foroperating relays 26 and 28 from common ground over wires 23 and 24 torelay windings and grounded battery. These relays complete the operatingcircuits of relays 22 and 30, 45 and 46, and their own locking circuitsas in recording. The operation of relay 22 operates relay 32 and by thesame sequence of operations as described in recording, relay 14 isrcleased and relay 47 operated. It should be noted, however, that 'inthe reproducing potentiometer the leads to the relays are reversed sothat relay 47 in this case adds resistance 12 to resistance 13 in theloud speaker circuit. This introduces a 10 TU gain in that circuit whichcompensates for the 10 TU loss inserted during the recording process.

In a similar manner markings corresponding to a 20, 30, or 40 TU loss inthe recording of varying the loss in the recording circuit according tothe limitations of the recording material, making a single record of thesounds, marking the recordat intervals only with code markings inaccordance with the loss inserted, reproducing the record and varyingthe gain in the reproducing circuit according to the markings.

2. In a recording and reproducing system a source of sound waves, afilm, means for translating said waves into electric currents, means formodifying said currents in accordance with the limitations of saidsystem, recording means for making a single record of said modifiedcurrents upon said film and marking said film at intervals only withcode markings representing the modifications of said currents,reproducing means for reproducing and remodiiying said currents'to theiroriginal values in accordance with said markings, and retranslatingmeans for translating said currents again into sound waves.

3. A method of recording a wide range of sound intensities whichconsistsintranslating the sounds to be recorded into correspondingelectric currents, amplifying the currents so that the sounds in thepianissimo range are represented by currents well above the lower limitof the recording medium, arbitrarily inserting when necessary sufficientloss in the recorder circuit to prevent the currents from exceeding theupper limit of the medium, making a single record of the currents, and

marln'ng the record at intervals only with code markings representingthe loss inserted. In witness whereof, I hereunto subscribe my name this13th day of December, A. D.

ROBERT C. MATHES.

circuit will actuate potentiometer relay 73,

74, or 75, to raise the volume level in the reproducing circuit acorresponding amount.

By making the contact fingers adjustable with respect to the soundrecord and arrang ing them in the proper relative location with respectto the reproducer, any slight differences in the time required for theoperation of thecompression and expansion systems can be readilycounteracted so that changes in

